This invention relates to the repair of strip conductors on electrical circuit boards and, more particularly, to the use of electrical sensing of position, and to optical alignment of a milling cutter used in surface preparation for soldering or braze repair of conductor material and removal of shorting material between conductors.
In the manufacture of printed circuit boards, electrical conductors are formed of metal strips produced by photolithography upon an insulating substrate. The conductors connect electrical components mounted on the circuit board, and may also be connected with further conductors on the opposite side of the substrate by means of vias. Frequently, it is desirable to conserve space on the printed circuit boards by constructing the conductors to be as narrow as practical, and to position the conductors closely together.
A problem arises in that the photolithographic process may not be perfect. There may be a deficiency of plated metal at a point on a conductor resulting in a break in the conductor. Furthermore, excessive metal may be found between two neighboring conductors resulting in a short between the two conductors. Such a break or such a short can cause a circuit to malfunction, and necessitate repair if the circuit board is to be utilized. If the break or short cannot be repaired, then the circuit board must be scrapped.
Attempts to repair such shorts and breaks have been only marginally successful because of the tedium and exactness required in manually manipulating tools for the preparation of the surface of the board for a soldering operation to repair the break, and for the removal of the shorting material. The chance of a successful repair diminishes with decreasing width of conductor and decreasing spacing between neighboring conductors. A particular aspect of the problem is the difficulty in the alignment and positioning of a tool which is suitable for removal of shorting material between conductors, as well as the positioning and alignment of a tool which can remove a protective coating and clean a conductor surface prior to a soldering or brazing repair operation.